This application claims priority from Japanese application serial no. 2002-102559, filed Apr. 4, 2002.
1. Field of the Invention
The present invention relates to a key switch structure for use in computer keyboards. More particularly, the present invention pertains to a thin-form key switch structure that is suitable for use in thin notebook-type personal computers or other low profile computers.
2. Description of the Prior Art
With the advent and popularity of thin, lightweight notebook-type personal computers, manufacturers have continuously sought to further reduce the size, weight and thickness of such computers. The size, height and weight of the key switches that are positioned under each keytop contribute significantly to the size and weight of notebook computers. Thus, manufacturers have attempted to achieve such reductions by developing thin-forming or low profile key switches. However, there are several constraints that make further reduction of the height and weight of the key switch very difficult. For example, for optimal operability a minimum keystroke length of 2.6 to 2.7 is required as well as a certain click sensation. Under such constraints, any significant additional height or weight reduction of key switches cannot be achieved using the conventional switches.
The key switch disclosed in JP Patent 2001-14083 is an example of a key switch which retains a fixed keystroke and click sensation. The main portions of this key switch are as shown, for example, in the vertical cross sections depicted in FIGS. 5 and 6 as well as in the stabilizer section of a conventional key switch as depicted in FIG. 7. FIG. 5 shows the key switch of Section Axe2x80x94A of FIG. 7 in the OFF state. FIG. 6 shows the same key switch but from a perspective of Section Bxe2x80x94B of FIG. 7 and in the ON state.
Referring to the key switch of depicted in FIG. 5, the key switch structure is comprised of reinforcing base plate 1, membrane switch 2 disposed on reinforcing base plate 1, frame 3 on membrane switch 2, stabilizer 4, key top 5, and click rubber 6 sandwiched between the membrane switch 2 surface and the key top 5 bottom surface. Membrane switch 2 includes two (flexible film) layers 8 and 9. Membrane switch 2 further includes spacer 7 that is positioned between membrane layers 8 and 9. Electrical contact 10 and electrical circuits are provided on the opposing surfaces of membrane layers 8 and 9. Hole 11 is an opening in spacer 7 at the location of the electrical contact 10. When membrane layer 8 is pushed downward in the area above electrical contact 10 membrane layer 8 is distorted downward placing electrical contact 10 in the ON state.
As shown in FIG. 7, stabilizer 4 is affixed on each of the left and right sides of the click rubber 6 (left and right as seen from the key switch operating position). Two long and narrow flat pieces 15 and 16 are arranged to form X-shaped part 18. Flat pieces 15 and 16 may be made from a rigid material such as metal, hard plastic or the like. Stabilizer 4 formed as X-shaped part 18 is linked at an intermediary point by a support axis 17 allowing stabilizer 4 to have a variable crossing angle xcex1. Slider 20 is circular and perpendicularly protrudes from the bottom end of each X-shaped part 18. Four sliding portions or sliders 20a-20d are contained in a free-fitting state within the square-shaped free motion range limiter 13 respectively located at four points around the hole 12 in frame 3.
The width W of the free motion range limiter 13 described above is slightly greater than the width of the slider 20. The length of free motion range limiter 13 must be relatively substantial in order to allow the bottom of key top 5 to make contact with the top surface of frame 3. Thus, slider 20 is able to move freely while sliding on the surface of membrane layer 8 within free motion range limiter 13. A stopper (not shown) projects over free motion range limiter 13 that contains slider 20, such that the slider 20 does not jump out of free motion range limiter 13.
Frame 3 identified above is affixed to the top of membrane switch 2 and has a flat shape. Hole 12 is an opening in frame 3 that is positioned above electrical contract 10 of membrane switch 2. Moreover, in addition to free motion range limiter 13, there is a slit shaped storage hole 21 for the X-shaped part that connects two free motion range limiters 13 on each side of click rubber 6. More specifically, X-shaped part storage hole 21a connects the two free motion range limiters 13 on one side of click rubber 6 and X-shaped part storage hole 21b connects the two free motion range limiters 13 on the other side of click rubber 6, as shown in FIG. 7. There is also a notch in storage hole 21 at the position at which stabilizers 4 are linked.
As shown in FIGS. 5-7, slider 22 is circular and protrudes perpendicularly from the both top ends of each X-shaped part 18. As shown in FIG. 5, slider 22 loosely fits within the horizontal part of L-shaped engagement piece 23 that is disposed at the four corners of the bottom surface of key top 5. The distance between hanging portion 24 on the side of key top 5 and the vertical portion of engagement piece 23 is sufficiently greater than the diameter of slider 22. This distance allows slider 22 to move freely between hanging portion 24 and vertical portion of engagement piece 23 while sliding on the bottom surface of key top 5 or on the horizontal portion of engagement piece 23.
X-shaped part 18 is linked to frame 3 and key top 5 so as to be able to move freely within a fixed range on the surface that contains it. The arrangement, dimensions, and shape of each of the parts which control the range of play are selected so that sliders 20 and 22 have a predetermined positional relationship to free movement range limiters 13 when key top 5 is in the OFF or normal state and in the ON or compressed state.
This prior art key switch design, however, has several disadvantages. As shown in FIG. 6, key top 5 may be depressed so that X-shaped part 18 is compressed until the crossing angle xcex1 is 180 degrees and key top 5 cannot be depressed further. At this point, lower end slider 20 of X-shaped part 18 is in a position whereby it contacts free motion range limiter 13 outside wall surface 13b, and top end slider 22 is in a position whereby it contacts key top 5 side hanging portion 24. As a result, further displacement is prevented and key top 5 is stopped at that position.
While the height reduction technique for the prior art key switch described above has affected the size and weight reduction of personal computers, frame 3 in such switches overlaps and tightly adheres to the upper portion of the membrane switch 2. As a result, even when free motion range limiter 13 outside wall surface 13b is extended and key top 5 bottom surface contacts the upper surface of frame 3, the overall key switch thickness cannot be brought below the sum of key top 5 height (including the side hanging portion 24) and the respective thickness of frame 3, membrane switch 2, and reinforcing base plate 1, thus limiting the ability to reduce key switch thickness or height further.
Another disadvantage is that although the spreading width W of free motion range limiter 13 is only slightly larger than the width of slider 20. However, a substantial amount of lengthwise space is required so as to allow key top 5 to make contact with the top surface of frame 3 when key top 5 is fully depressed. As a result of this substantial lengthwise space in free motion limiter 13, when key top 5 is depressed the direction of movement for key top 5 differs depending on whether the force applied to key top 5 is exerted towards a the keyboard operator or away from the keyboard operator. In other words, key top 5 makes undesirable movements in the frontward or backward direction depending on the degree of force exerted by the keyboard operator when pressing down on a key top.
Accordingly, the object of the present invention is to eliminate some of the disadvantages found in the prior art and to provide a low profile key switch structure that is substantially reduced in height so as to reduce the thickness of personal notebook computer or the like. Another object of the present invention is to provide a key switch structure that minimizes undesirable key top movement that occurs when the key is depressed and which varies depending on the direction of the force that is exerted on the key top at that time.
In general, the first aspect of the present invention features a key switch structure that includes, a key top, a click rubber having a resilient force that pushes the key top upward when the key top is depressed and a membrane switch which disposed under the click rubber. This key top switch structure also includes a reinforcing base plate disposed on the bottom of the key switch structure, a pair of stabilizers disposed between the reinforcing base plate and the bottom surface of the key top wherein the pair of stabilizers are arranged so that there is one stabilizer on each side of the click rubber and a pair of stabilizer holders are formed at opposing ends of the bottom of the key top so that each stabilizer holder can hold one top end of each stabilizer.
This invention further includes a pair of frames that are arranged so that each said frame supports one stabilizer, a pair of top free motion range limiters are each formed between the stabilizer holder and the key top for each stabilizer wherein the top free range motion limiter is further formed to enclose a first top end and a second top end of each stabilizer therein in a free fitting manner. Similarly, the key switch structure of the present invention further includes a pair of bottom free motion range limiters are formed on each frame so that the bottom of each free motion range limiter engages with and is affixed to a free range limiter engagement section wherein the free motion range limiting engagement section is formed within the reinforcement base plate. The pair of bottom free-range motion limiters is further formed to enclose a first bottom end and a second bottom end of each stabilizer therein in a free fitting manner. The frame and the membrane switch are affixed on the reinforcing base plate so that the frame and the membrane switch do not overlap.
Embodiments of the invention may include one or more of the following features: a key switch structure wherein the first and second top ends and the first and second bottom ends of each of the stabilizers have sliders that projects perpendicularly therefrom so as to be enclosed in the pair of top free motion range limiters and the pair of bottom free motion range limiter.
Another embodiment may include a key switch structure, wherein each stabilizer is formed by two flat pieces that are joined at an intermediary point using an intermediary support axis so as to provide each stabilizer with a variable crossing angle that varies with the vertical movement of the key top.
Another embodiment may include a key switch structure, wherein a pair of top free motion range limiters and a bottom pair of free motion range limiters include a front and a rear free motion range limiter.
Another embodiment may include a key switch structure, wherein the slider of the first top end and the first bottom end of each stabilizer are allowed to rotate within each the front free motion range limiters and wherein the slider of each second top end and the second bottom end of each stabilizer is formed so as to allow the slider to rotate and slide within each rear free motion range limiters.
Another embodiment may include a key switch structure, wherein the key top further includes a convex section that protrudes downward from the bottom side of the key top and that is formed to fit that top portion of the click rubber.
Another embodiment may include a key switch structure, wherein the key top further includes a pair of engagement parts that project downward from the bottom side of opposing ends of the key top. Each engagement part has a protuberance that projects from its bottom that supports the stabilizer holder.
Another embodiment may include a key switch structure, wherein the free motion range engagement limiting section further includes a set of three vertical walls that limit the range of sliders on the bottom of each stabilizer.
Another embodiment may include a key switch structure, wherein the free motion range engagement limiting section further includes a pair of support columns that engage each frame.
Another embodiment may include a key switch structure, further includes notches that are formed in each frame to enclose sliders that engage each the frame.
Another embodiment may include a key switch structure, further includes notches that are formed on the reinforcement base plate to enclose the bottom end of the flat piece of each stabilizer.
Another embodiment may include a key switch structure, further includes a concave section that is formed to engage the engagement parts when the key top is depressed so that the engagement parts do not make contact with the membrane switch or frame.
The above advantages and features are of representative embodiments only. It should be understood that they are not to be considered limitations on the invention as defined by the claims.